Question

Choose the correct statement regarding electrolysis of water from the options given below.

• A. The gas released at anode is hydrogen.
• B. The gas liberated at cathode is double the volume of gas liberated at the anode.
• C. The gas liberated at cathode is half the volume of gas liberated at the anode.
• D. The gas released at cathode is oxygen.

Answer 1

The correct option is B The gas liberated at cathode is double the volume of gas liberated at the anode.

The chemical formula of water is ${\text{H}}_2\text{O}$. During its electrolysis, the water molecule undergoes decomposition to form ${\text{H}}^{+}$ and ${\text{OH}}^{-}$ ions.

The ${\text{H}}^{+}$ ions move towards the cathode (negatively charged electrode) and thus hydrogen gas evolves there. The reaction occuring at cathode is:

$2{\text{H}}_2\text{O (l)}+2{\text{e}}^{-}\to {\text{H}}_2\text{(g)}+2{\text{OH}}^{-}\text{(aq)}$

The ${\text{OH}}^{-}$ ions move towards the anode (positively charged electrode) and thus oxygen gas evolves there. The reaction occuring at anode is:

$2{\text{H}}_2\text{O (l)}\to {\text{O}}_2\text{(g)}+4{\text{H}}^{+}\text{(aq)}+4{\text{e}}^{-}$

The composition of hydrogen in water is double than that of oxygen (2:1 ratio). Thus, the volume of gas collected at cathode $\left({\text{H}}_2\right)$ is double than volume of gas collected at anode $\left({\text{O}}_2\right)$.